Rotate or Replace the Mixing Tube
Although the mixing tube is made from an extremely hard material, over time, the flow of high-pressure water and garnet abrasive will wear away the inside of the mixing tube . This results in a gradual, irregular widening of the internal diameter of the mixing tube, causing a less accurate stream of garnet abrasive and water. A cross section of these mixing tubes reveals the irregular wear of their internal diameter. Examples of normal , good , and bad  mixing tube wear are shown below
The mixing tube is very brittle and easily broken if dropped or struck hard. The key to a long mixing tube life is maintaining a healthy orifice or jewel. Damage to mixing tubes caused by misaligned jets or a damaged jewel is not apparent when looking through the bore of the mixing tube. The size of the kerf and cutting performance are the best indicators of mixing tube wear. The kerf is the width of the cut made by the abrasive waterjet. With a 0.030 in. (0.762 mm) mixing tube, it can range from 0.015 in. (0.38 mm) to 0.060 in. (1.52 mm), depending on the nozzle, the thickness of the material being cut, and the amount of wear on the mixing tube.
A clogged mixing tube is most frequently caused by using contaminated garnet abrasive. Because the opening in the mixing tube is small, even a small particle of dirt can clog it. Other potential causes of clogging include contaminated or wet garnet abrasive. Metal chips from other shop operations and paper from the garnet abrasive bag are two common sources of contamination. To clear a clogged mixing tube, see 401434-EN Operation, ProtoMAX.
1. Open the lid and lock it in the upright position.
Use care when opening or closing the lid to avoid injury. Never let the lid free-fall. Keep hand, fingers, or body parts away from the side of the table when closing the lid.
2. Place a piece of cardboard or similar material on the cutting deck to keep the mixing tube from falling in the catcher tank.
3. Remove the nozzle splash guard .
4. Clean and inspect the splash guard for damage, replace as needed.
5. Loosen the mixing tube retainer  and replace or rotate the mixing tube  90 degrees (one-quarter turn).
6. Verify the mixing tube is properly seated into the nozzle body and tighten the mixing tube retainer.
7. Close the lid.
8. Perform a nozzle test, see Test the Nozzle.